Near-infrared imaging InGaAs sensors show lower performances in term of noise and sensitivity compared to silicon based cameras. Image frequency conversion from near-infrared to visible wavelengths by nonlinear parametric sumfrequency mixing in a χ(2) medium should increase detection performances in active imaging applied to long range target identification. For such applications, both energy conservation and phase matching conditions are ideally suited to efficient upconversion. Nevertheless, the available resolution still hampers the development of upconversion imagers.

In this paper, we upconvert images provided by 1.5 μm collimated continuous wave lasers illuminating resolution targets and small objects. Using a 2.7 nm wide pump spectrum at 1064 nm, we resolve 56x64 spatial elements whereas we obtained only 16x19 spatial elements with a narrow spectrum pump laser at 1064 nm with the same beam diameter and 8x8 spatial elements with a 0.5 mm thick crystal. These results are compatible with long range target recognition. A laboratory scale experiment of active imaging of diffusive objects is shown as an illustration.

Unlike photographic image sensors with infrared cutoff filter, low light image sensors gather light over visible and near infrared (VIS-NIR) spectrum to improve sensitivity. However, removing infrared cutoff filter makes the color rendering challenging. In addition, no color chart, with calibrated infrared content, is available to compute color correction matrix (CCM) of such sensors. In this paper we propose a method to build a synthetic color chart (SCC) to overcome this limitation. The choice of chart patches is based on a smart selection of spectra from open access and our own VIS-NIR hyperspectral images databases. For that purpose we introduce a fourth cir dimension to CIE-L*a*b* space to quantify the infrared content of each spectrum. Then we uniformly sample this L*a*b*cir space, leading to 1498 spectra constituting our synthetic color chart. This new chart is used to derive a 3x4 color correction matrix associated to the commercial RGB-White sensor (Teledyne-E2V EV76C664) using a classical linear least square minimization.. We show an improvement of signal to noise ratio (SNR) and color accuracy at low light level compared to standard CCM derived using Macbeth color chart.

We present an embedded imaging approach based on low cost sensors that span a long spectral range in the infrared. A system has been implemented with 12 apertures that combine unique uncooled FPAs in the mid infrared domain -2 to 5 microns wavelength- with very low cost microbolometers in the thermal infrared -7 to 14 microns wavelength-. Both FPA technologies are uncooled and low cost, manufactured as monolithic devices. The system is made of two modules, one LWIR, other MWIR. Each module has a system-on-chip GPU/ARM board that carries out all the image processing required for image reconstruction. This includes the calibration of the system, the registration of the images acquired with the many apertures, and the reconstruction of the super resolved image. Besides, the board performs all the operations and transformations required for noise correction. The output of each of the modules is a video stream at 30 frames per second. Each frame is a super resolved image with a resolution 2.5x compared to the images acquired by the FPAs used. Furthermore, the modules may be integrated and the acquired images combined in a single one in the embedded processing boards. Moreover, the boards may also combine and fuse this output with a visible range video stream. The use of low cost FPAs facilitates the deployment in a broad range of applications that an benefit from imaging in the infrared, particularly in the MWIR range in which existing commercial cameras based on hybrid technology are very expensive. The system is being tested in different applications, including surveillance in variable lighting conditions and monitoring in firefighting scenarios

We propose a technique based on a transmission grating placed in front of an imaging system (e.g. a telescope) mounted on a frame that can be rotated around the optical axis. The grating creates, for each point of the source image (e.g. a star), at the focal plane, an image composed by the undistorted image of the star plus symmetrical dispersion images of several diffraction orders. The grating is rotated and several images are captured for different angular positions of the same. By analyzing the different images obtained for a different grating angle, it is possible to build the hyperspectral cube. The advantages of this method is its simplicity, extreme compactness and low cost making it suitable both for amateur astronomy and low budget science laboratory. We will present preliminary experimental results along with a discussion about the achievable spectral and spatial resolution and photon collection efficiency as a function of different type of gratings and of the number of the captured pictures. Furthermore, we present the result when the method is applied to extended non-punctiform light sources.

One of the most peculiar features of imaging systems is the trade-off between resolution and depth of field. Resolution can be improved by increasing the numerical aperture of the imaging system. However, the range of distances that can be put in sharp focus in a single shot decreases with the square of the numerical aperture. Plenoptic imaging (PI) devices are able to retrieve both spatial and directional information from the scene of interest, usually by placing a microlens array in front of the camera sensor. This feature entails the possibility to refocusing planes of the scene in a much wider range than the natural depth of field of the system, and also to change the point of view on the scene. Though plenoptic imaging is one of the most promising techniques for 3D imaging, its advantages come at the expense of spatial resolution, which can no longer reach the diffraction limit. We experimentally demonstrate that correlations of chaotic light can be exploited to overcome the inverse proportionality between depth of field and resolution, and perform plenoptic imaging at the diffraction limit. We retrieve images by correlating intensity fluctuations at different points of two parts of a sensor, which register spatial and angular information, respectively. Hence, our Correlation Plenoptic Imaging (CPI) protocol does not add any limitation to the native resolution of the imaging system. We show the experimental refocusing, through the CPI procedure, of widely out-of-focus parts of a transmissive test target. Moreover, we determine and test the theoretical limits of CPI in terms of resolution and depth of field, quantifying the improvement with respect to standard imaging and classical PI. We finally comment on future perspectives.

We propose to add an optical component in front of a conventional camera to improve depth estimation performance of Depth from Defocus (DFD), an approach based on the relation between defocus blur and depth. The add-on is an afocal doublet, which adds chromatic aberration to the global system. This overcomes ambiguity and dead zone, which are the fundamental limitations of DFD with a conventional camera since the blur become unambiguous and measurable for each depth. In this paper we present the principle of the add-on, a theoretical performance model and experiments on real prototype to illustrate the improvement of depth estimation performance with the proposed add-on.

Automated visual inspection of transparent objects is important for many industrial fields. Especially the detection of scattering impurities inside complexly shaped transparent objects is a demanding task. Usually, so-called dark field approaches are employed in this case. However, these methods often fail due to direct reflections of the light sources, e.g., at the test object's surface which cannot be distinguished from signals of real material defects. This paper introduces an inspection approach which captures images at different illumination modalities and fuses them while optimizing the signal-to-noise ratio. Two fusion strategies are presented, which employ prior knowledge in order to obtain optimized inspection images. The signal component of the observed images is defined as the signal corresponding to visualized defects. Conversely, all light reaching the sensor due to scattering or reflections caused by the test object's geometry is regarded as noise. The signal values and noise values depend on both the pixel position and the respective illumination source. Prior knowledge about the signal and noise components allows to estimate the spatially resolved SNR for every illumination channel. The images resulting from the fusion step show scattering material defects with high contrast whereas surface reflections are nearly completely mitigated by the SNR-optimized fusion strategies. Several experiments state the performance of the presented approaches.

In remote sensing, a common scenario involves the simultaneous acquisition of a panchromatic (PAN), a broad-band high spatial resolution image, and a multispectral (MS) image, which is composed of several spectral bands but at lower spatial resolution. The two sensors mounted on the same platform can be found in several very high spatial resolution optical remote sensing satellites for Earth observation (e.g., Quickbird, WorldView and SPOT)

In this work we investigate an alternative acquisition strategy, which combines the information from both images into a single band image with the same number of pixels of the PAN. This operation allows to significantly reduce the burden of data downlink by achieving a fixed compression ratio of 1/(1+b/p2) compared to the conventional acquisition modes. Here, b and p denote the amount of distinct bands in the MS image and the scale ratio between the PAN and MS, respectively (e.g.: b = p = 4 as in many commercial high spatial resolution satellites). Many strategies can be conceived to generate such a compressed image from a given set of PAN and MS sources. A simple option, which will be presented here, is based on an application of the color filter array (CFA) theory. Specifically, the value of each pixel in the spatial support of the synthetic image is taken from the corresponding sample either in the PAN or in a given band of the MS up-sampled to the size of the PAN. The choice is deterministic and done according to a custom mask. There are several works in the literature proposing various methods to construct masks which are able to preserve as much spectral content as possible for conventional RGB images. However, those results are not directly applicable to the case at hand, since it deals with i) images with different spatial resolution, ii) potentially more than three spectral bands and, iii) in general, different radiometric dynamics across bands. A tentative approach to address these issues is presented in this work. The compressed image resulting from the proposed acquisition strategy will be processed to generate an image featuring both the spatial resolution of the PAN and the spectral bands of the MS. This final product allows a direct comparison with the result of any standard pan-sharpening algorithm; the latter refers to a specific instance of data fusion (i.e., fusion of a PAN and MS image), which differs from our scenario since both sources are separately taken as input. In our setting, the fusion step performed at the ground segment will jointly involve a fusion and reconstruction problem (also known as demosaicing in the CFA literature). We propose to address this problem with a variational approach. We present in this work preliminary results related to the proposed scheme on real remote sensed images, tested over two different datasets acquired by the Quickbird and Geoeye-1 platforms, which show superior performances compared to applying a basic radiometric compression algorithm to both sources before performing a pan-sharpening protocol. The validation of the final products in both scenarios allows to visually and numerically appreciate the tradeoff between the compression of the source data and the quality loss suffered.

Single-pixel imaging based on structured illumination and compressed sensing has opened a new way to compress massive imaging data volume and significantly reduce the cost of image sensor without sacrificing imaging quality. However, conventional structured illumination methods based on digital micro-mirror device (DMD) or a liquid crystal based spatial light modulator (SLM) fall short in fresh rate, making it a real challenge for high-speed imaging applications, which are however of paramount importance in studying dynamic phenomena in living cells, neural activity, and microfluidics, and capturing important rare events.
In this work, we propose and demonstrate a new approach for ultrafast (20 Mfps) structured illumination single-pixel imaging using light beam speckles out of a multimode fiber due to multimode interference. Our experimental results show that the excited high-order modes, and hence the multimode interference, are strongly wavelength-dependent. Update of the random speckle patterns can be easily obtained by sweeping the incident wavelength. Ultrafast wavelength sweeping is achieved by stretching ultrafast optical pulses from a mode-locked laser using chromatic dispersion. Extremely broad bandwidth and small wavelength step guarantee a good number of illumination patterns. By measuring multiple dot products of a sparse image with a set of known speckle based random, the image can be reconstructed using an L1 minimization algorithm.
The most significance of this completely new design is that multiple (up to thousands) structured illumination measurements can be carried out within a single pulse period, enabling ultrafast pulse-by-pulse imaging. Moreover, thanks to structured illumination and compressed sensing, the proposed structured illumination single-pixel imaging system offers much higher imaging resolution than existing ultrafast photonic time stretch imaging systems for the same captured data size.

Diffuse Optical Tomography (DOT)is a powerful tool for the reconstruction of optical properties inside a diffusive medium, such as biological tissues. In particular, in the last years, techniques based on structured light illumination and compressive sensing detection have been developed. In this work a time-resolved system based on structured light illumination and compressive detection has been developed and used for DOT. Moreover, a data-driven algorithm for optimal pattern generation based on the Singular-Value Decomposition has been implemented and validated.

We present the design, calculations and simulations of high-resolution concave-VLS-grating-based soft X-ray and VUV spectrographs, as well as a plane VLS grating instrument. We have designed a normal-incidence imaging VLS grating spectrograph for a 820 – 1690 Å spectral interval and a series of grazing-incidence VLS spectrographs with imaging capabilities. The experimentally recorded spectral images of laboratory laser plasmas were obtained with the aid of a VLS spectrometer based on a concave aperiodic multilayer mirror and a plane VLS grating. Two modifications of this spectrometer were implemented with two different VLS gratings. These modifications exhibit spectral resolution of 500 and 800 over the 125 – 300 Å spectral waveband. Spatial resolution corresponds to double CCD-detector pixel size.

Nowadays, the stereoscopic endoscopy is a widely used tool for precise three-dimensional (3D) measurements of hard-to-reach elements in industrial and biomedical applications. The most common approach for its implementation is the utilization of prism-based optical tips which allow to acquire two images from different viewpoints on a single sensor. Stereo video endoscopes are typically equipped with a wideband white light source, but contrast visualization of the inspected object and, therefore, accurate quantitative characterization of its parameters often requires narrow band spectral imaging. We show that the standard geometrical calibration may lead to significant measurement errors when obtained using white illumination and applied to narrow band images. In order to overcome this, we propose the new calibration procedure based on a proper choice of a few spectral bands for calibration and interpolation of the calculated parameters. Results of multiple experiments show that the proposed technique fosters the measurement accuracy increase.

I review our latest off-axis holographic compression techniques for quantitative phase microscopy of dynamic cells. Offaxis holography allows quantitative acquisition of live cells without staining, by reconstructing their quantitative phase profile from a single camera exposure. In this technique, one of the interfering beams is slightly tilted relative to the other beam, creating separation of the field intensity from the two conjugate wave front terms in the spatial-frequency domain. We showed that this encoding leaves a lot of empty space in the spatial-frequency domain, into which additional information can be compressed. This compression can be done using optical multiplexing of up to six complex wave fronts into a single camera plane, where each pair of sample and reference beams creates an off-axis hologram with a different interference fringe direction that positions the wave fronts in the spatial frequency domain without overlapping with any other term. This new holographic compression approach is useful for various applications, with focus on quantitative phase acquisition of fast cellular dynamics, including imaging cells during rapid flow. I present several experimental systems that implement this holographic compression approach, and review various applications.

This paper proposes digital holographic microscopy applied to the study of the production of lipids in Chlorella vulgaris microalgae. We propose to use several wavelengths to establish a chromatic phase contrast being the signature of the presence, or absence, of lipids in a set of microalga culture. In order to achieve this goal, the 3-color microscope has to be perfectly calibrated so that a point-to-point chromatic contrast can be evaluated without any distortion due to aberrations. The analysis of chromatic phase contrasts leads to measure the experimental probability density functions of the chromatic phase contrast distribution. Statistical analysis of the phase distribution in stressed cells and for not stressed cells reveals a difference in the probability densities. These experimental curves are fitted with two different theoretical modeling, one for the stressed algae (production of lipids), and one other for not-stressed algae. Fitting to experimental data demonstrates that the proposed approach opens the way for an in-situ and non-destructive experimental method to evaluate the production rate of lipids from Chlorella vulgaris algae.

Tomographic Diffractive Microscopy (TDM) is an advanced digital imaging technique, extending the concept of Digital Holographic Microscopy (DHM), which provides quantitative information about the index of refraction distribution within the observed sample, by recording of multiple holograms under varying conditions of illumination, then applying numerical inversion procedures to reconstruct a 3-D image of the specimen under consideration. After a short recall of DHM applications and limitations, various implementations of TDM are described, highlighting their respective advantages and. drawbacks. To conclude, some perspectives and challenges for this imaging modality are presented.

This paper reports on advances in optical coherence tomography (OCT) for application in dermatology. Full-field OCT is a particular approach of OCT based on white-light interference microscopy. FF-OCT produces en face tomographic images by arithmetic combination of interferometric images acquired with an area camera and by illuminating the whole field of view with low-coherence light. The major interest of FF-OCT lies in its high imaging spatial resolution (∼ 1.0 μm) in both lateral and axial directions, using a simple and robust experimental arrangement. Line-field OCT (LFOCT) is a recent evolution of FF-OCT with line illumination and line detection using a broadband spatially coherent light source and a line-scan camera in an interference microscope. LF-OCT and FF-OCT are similar in terms of spatial resolution. LF-OCT has a significant advantage over FF-OCT in terms of imaging penetration depth due to the confocal gate achieved by line illumination and detection. B-scan imaging using FF-OCT requires the acquisition of a stack of en face images, which usually prevents in vivo applications. B-scan imaging using LF-OCT can be considerably faster due to the possibility of using a spatially coherent light source with much higher brightness along with a high-speed line camera. Applied in the field of dermatology, the LF-OCT images reveal a comprehensive morphological mapping of skin tissues in vivo at a cellular level similar to histological images.

Phase retrieval reconstruction is a central problem in digital holography, with various applications in microscopy, biomedical imaging, fluid mechanics. In an in-line configuration, the particular difficulty is the non-linear relation between the object phase and the recorded intensity of the holograms, leading to high indeterminations in the reconstructed phase. Thus, only efficient constraints and a priori information, combined with a finer model taking into account the non-linear behaviour of image formation, will allow to get a relevant and quantitative phase reconstruction. Inverse problems approaches are well suited to address these issues, only requiring a direct model of image formation and allowing the injection of priors and constraints on the objects to reconstruct, and hence offer good warranties on the optimality of the expected solution. In this context, following our previous works in digital in-line holography, we propose a regularized reconstruction method that includes several physicallygrounded constraints such as bounds on transmittance values, maximum/minimum phase, spatial smoothness or the absence of any object in parts of the field of view. To solve the non-convex and non-smooth optimization problem induced by our modeling, a variable splitting strategy is applied and the closed-form solution of the sub-problem (the so-called proximal operator) is derived. The resulting algorithm is efficient and is shown to lead to quantitative phase estimation of micrometric objects on reconstructions of in-line holograms simulated with advanced models using Mie theory. Then we discuss the quality of reconstructions from experimental inline holograms obtained from two different applications of in-line digital holography: tracking of an evaporating droplet (size~100μm) and microscopy of bacterias (size~1μm). The reconstruction algorithm and the results presented in this proceeding have been initially published in [Jolivet et al., 2018].1

We propose a new detection scheme for Spectral Optical Coherence Tomography (SOCT) that allows for a single shot depth-dependent visualization of spectroscopic properties of imaged objects. Compared to commonly used methods based on short time Fourier transformation or recently proposed technique based on Spectral and Time domain Optical Coherence Tomography (STdOCT) [1] it offers increased sensitivity and resistance to motion artefacts.
The proposed method, called single shot Spectral and Time domain Optical Coherence Spectroscopy (ssSTdOCS), is based on spectroscopic version of STdOCT, but uses a 2D detector in the spectrometer and thus allows for registration of a complete data set in a single acquisition event.
Originally we proposed STdOCS as an alternative for commonly used methods based on short time Fourier transformation. The method utilizes spectral OCT setup with a spectrometer equipped with linescan CCD or CMOS camera as the detector. During the measurement continuous change in optical path difference between the two arms of OCT interferometer is introduced by an optical delay line in the reference arm. Resultant sequence of spectra is subject to 2D Fourier transformation that provides the representation of the OCT signal in “Doppler frequency” – “depth” space. The signal along Doppler frequency axis has envelope corresponding to the spectrum of the light coming back from particular depth in the object. In this aspect it can be regarded as spatially resolved Fourier transform spectroscopy.
The measurement scheme required by STdOCS is sensitive to the internal motion of the imaged object, since the resultant 2D data set is built from the interference spectra acquired in time. To avoid this problem we propose here a modification of the measurement instrument. To acquire the whole 2D data set used in STdOCS we propose a spectrometer equipped with 2D array sensor. The broadband light from the superluminescent diode is collimated and brought to the input of Mach-Zehnder interferometer. In the object arm the beam is focused by the objective lens in the object plane and the light scattered within the object is brought to interference with the reference beam in the output beamsplitter. The beams from reference and object arms of the interferometer are incident on the diffraction grating at relative angle in the plane determined by the grating lines and the optical axis. In the perpendicular plane the diffraction angles were the same for both beams. In the reference arm the pair of kinematic mirrors provides the possibility of precise adjustment of the angle between the beams. The first diffraction order is focused on the CCD camera with the use of cylindrical achromatic doublet. In the resulting 2D interferogram each horizontal row contains interferometric spectra with different optical path differences between the optical paths of the reference and object beams resulting from different angles of incidence at the CCD plane. This single-shot exposure event provides data sufficient for STdOCS analysis scheme.
We show that the effective quantitative measurement of the depth-dependent absorption spectra of indocyanine green solution placed in glass capillary is possible with the use of our method.
1. Maciej Szkulmowski, Szymon Tamborski, Maciej Wojtkowski, "Spectroscopy by joint spectral and time domain optical coherence tomography," Proc. SPIE 9312, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XIX, 93122P (2 March 2015);

The study of bioimaging with controlled depth using upconversion nanoparticles under near-infrared excitation was performed in this work. Monte Carlo simulation was performed to determine optimal distance between the fiber - source of laser radiation, and the receiving fiber for obtaining the signal from maximal depth in biological tissue. Also theoretical modeling of the spatial distribution of diffusely scattered radiation inside the tissue depending on wavelength is presented. Penetration depth for wavelengths corresponding to the upconversion luminescence was calculated.

Experimental modeling was carried out on phantoms of biological tissues simulating their scattering properties as well as accumulation of the investigated nanoparticles doped with rare earth ions. Measurements were performed using NaGdF4 nanoparticles doped with Yb3+, Er3+ and Tm3+ rare earth ions, which demonstrated several luminescence bands from the blue (475nm) to the near-infrared (800 nm) regions of the spectrum under 980 nm excitation. The different penetration depth of various wavelengths in biotissue allows us to estimate the depth from which the signal was obtained using luminescence intensity ratio (LIR). Due to non-linearity of upconversion process, pumping power dependences of luminescence intensity was taken into account. The number of involved photons for each spectral band was estimated and intensity ratio of emission bands was calculated. Based on calculations and experimental measurements, the theoretical and experimental luminescence intensity ratio for different depths was estimated. The experimental study was performed on biological tissue phantoms containing Lipofundin® with red blood cells and has shown good agreement with calculations. The use of theoretically calculated LIR allows us to solve the inverse problem and estimate the depth from which the signal was obtained.

Recent technological developments in ultrafast laser physics have permitted to make new kind of nonlinear microscopies, as microscopy based on Stimulated Raman scattering. These techniques are based on vibrational contrast mechanism for imaging with high sensitivity, high spatial and spectral resolution and 3D sectioning capability. The interest in the study of lipids and the possibility to image lipid droplets, thanks to their isolated Raman peaks associated with vibrational C-H bond, have encouraged investigation and identification of lipid structures inside cells, taking advantage of Stimulated Raman Scattering (SRS) imaging. In this work, we report and discuss label free images on biological environmental and structural analysis, to detect lipid microstructures inside adipocyte cells.

We present a partial application space of the metrology method referred to as through-focus scanning optical microscopy (TSOM), with most number of favorable attributes as a metrology and process control tool. TSOM is a NIST-developed, high-throughput and low-cost optical metrology tool for dimensional characterization with sub-nanometer measurement resolution of nano-scale to microscale targets using conventional optical microscopes, with many unique benefits and advantages. In TSOM the complete set of out-of-focus images are acquired using a conventional optical microscope and used for dimensional analysis. One of the unique characteristics of the TSOM method is its ability to reduce or eliminate optical cross correlations, often challenging for optical based metrology tools. TSOM usually has the ability to separate different dimensional differences (i.e., the ability to distinguish, for example, linewidth difference from line height difference) and hence it is expected to reduce measurement uncertainty.

Flow cytometry is a well-established technique that is widely applied in numerous fields, including pathology, pharmacology, immunology, marine biology, plant biology, and molecular biology. Conventional methods for flow cytometry fail to accurately detect cellular phenotypic characteristics due to a limited number of variants and the lack of spatial metrics. Imaging-based cell analysis methods, such as high-content screening and imaging flow cytometry, are advantageous over those univariate or few-variate methods because they offer the capability of acquiring multi-dimensional information of single cells, from which cellular characteristics can be detected with high accuracy and high specificity. However, currently available imaging flow cytometry methods suffer from low throughput which is mainly limited by the imaging techniques, or specifically, the frame rate of the commercial imaging sensors, such as CCD or CMOS sensors. In order to address these problems, here we present optofluidic time-stretch microscopy with extremely high throughput which is capable of acquiring bright-field images of large populations of cells with a high spatial resolution of 780 nm and a high throughput of >1 million cells/s, which is two orders of magnitude higher than conventional univariate or few-variate flow cytometry methods and three orders of magnitude higher than other imaging flow cytometry methods. This is made possible by integrating an optical time-stretch microscope with a hydrodynamic-focusing microfluidic device. In addition, we apply machine-learning algorithms to the acquired images to extract multiple morphological features from each cellular image to identify and classify the cells in a label-free manner with accuracy higher than 90%, which is comparable with the fluorescence-based methods. Specifically, we experimentally performed optofluidic time-stretch microscopy to detect K562 cells (leukemia cell line) spiked in whole blood samples which were treated with different concentrations of anti-cancer drugs. In the experiment, more than 10,000 high-quality images of K652 cells were acquired for each concentration of the drug. With machine-learning-based image processing and analysis, 548 morphological features were extracted from each image to comprehensively evaluate its cellular phenotypes and hence dose-dependent morphological changes of the cells caused by the drug treatment. We further confirmed the dose-dependent results in different experimental trials where the cells were treated with the drugs for different time spans. This is potentially applicable for research of cellular drug responses directly with whole blood, hence, beneficial to drug discovery and drug screening. With such high throughput, high performance and good compatibility with existing techniques, we believe that optofluidic time-stretch microscopy with extreme throughput will revolutionize the flow cytometry field and play an integral role in high-throughput, high-accuracy, and label-free cell screening in the future.

Glass formation and glassy behavior remain areas of investigation in soft matter physics with many aspects which are still not completely understood, especially at the nanometer size-scale and close to the glass transition temperature. In the present work, we show an extension of the “nanobubble inflation” method developed by O’Connell and McKenna [Rev. Sci. Instrum. 78, 013901 (2007)] which uses an interferometric microscope (white light scanning interferometry method) to measure the surface topography of a large array of 5 μm sized nanometer thick films. These so-called free-standing films are subjected to constant inflation pressure during which the nanobubbles grow or creep with time. Measurements of multiple bubbles in real time are possible via the technique of Phase Shifting Microscopy (PSM) thanks to the fast acquisition and processing of interferometry. This has been implemented using in-house developed LabVIEW based software combined with the IMAQ Vision module. Moreover this technique has the advantage, over the AFM method of O’Connell and McKenna, to be a true non-contact technique. Using this optical configuration, there is no substrate interaction to affect the polymer chains. Here we demonstrate the method using ultra-thin films of both poly(vinyl acetate) (PVAc) and polystyrene (PS) and discuss the capabilities of the method in comparison to AFM, with its advantages and disadvantages. The viscoelastic responses of the nanobubbles are determined by measuring their time-dependent diameters and then by extracting both the stress and strain time-dependent components (here the history of the polymer films has to be taken into account). We show that the results from experiments on PVAc are consistent with the prior work on PVAc. However high stress results with PS show signs of a new non-linear response regime that could be related to the plasticity of the ultra-thin film. Our homemade setup used to apply stresses on the films is also described. This first allows the control of both temperature, using a Peltier ring which surrounds the sample, and pressure, using gas flow linked to a manometer. Then major improvements of our setup in order to solve small experimental issues are described. Finally, plans for further improvements to the cell are explained for future experiments.

Multiphoton microscopy (MPM) is a recent method of imaging especially adapted to the imaging of samples of life sciences thanks to its ability to generate 3D images, with an interesting contrast and a low level of photodamage thanks to the range of wavelengths involved in the near infrared. This last point is crucial in the field of laser source development. Indeed, it has been recently identified that many new laser sources are adapted in their parameters to generate images by a multiphoton process. This results in the recent and fast increase of the quantity of laser sources especially dedicated to MPM with sometimes a focus on a specific multiphoton process. This article is an updated review of the laser sources involved in MPM in order to complete the previous one already published in 2017. Now, a focus on the new laser sources that can be listed during the two last years is proposed. We can see that a ten of drastically different and new laser sources are listed during the two last years. Is MPM dedicated to biomedical application a sufficiently broad topic with a sufficiently high level of market allowing to warrant such high level of investment in research-time and in laser development with the highest performances? Would not there be other scientific fields requiring such level of investments? Are these laser performances really identified and considered at their true level by the scientists who need MPM?

Conventional optical microscopes, such as brightfield, darkfield, phase contrast or differential interference contrast microscopes are partially coherent imaging systems. Imaging in a partially coherent system was first analyzed by Hopkins only in 1953. He propagated the mutual intensity through the optical system, but did not give an expression for the mutual intensity of the image itself. The mutual intensity is a four dimensional (4D) quantity that contains information about the modulus and phase of the image wave field, which depends on the object’s complex refractive index in 3D. The mutual intensity is related to other representations such as the Wigner distribution function (WDF) and ambiguity function. Explicit expressions for different phase space representations of the image wave field are given. The expressions separate into system and object dependent parts. In addition, explicit relationships between the defocused partially coherent cross-coefficient and phase space representations in the image plane are derived.

A model describing the signal generation in chromatic confocal imaging is presented here. It can be used to understand the signal development process accounting for wave-optical phenomena using scalar wave theory. The influence of the optics in terms of aberrations, the specimen in terms of roughness and further parameters on the signal generation process will be investigated. Moreover, the possibility to adapt the model to investigate other spectral imaging systems, such as chromatic confocal spectral interferometry will also be shown.

Because the inverse problem in diffuse optical tomography (DOT) is highly ill-posed in general, appropriate regularization based on prior knowledge of the target is necessary for the reconstruction of the image. The total variation L1 norm regularization method (TV-L1) that preserves the boundaries of a target is known to have excellent result in image reconstruction. However, large computational cost of the TV-L1 prevents its use in portable applications. In this study, we propose a dimension reduction method in DOT for fast and hardware-efficient image reconstruction. The proposed method is based on the fact that the optical flux from a light source in a highly scattering medium is localized spatially. As such, the dimension of a sensitivity matrix used in the forward model of the DOT can be reduced by eliminating uncorrelated subspaces. The simulation results indicate up to 96.1% reduction in dimensions and up to 79.3% reduction in runtime while suppressing the reconstruction error below 2.26%.

The mathematical phenomenon of super-oscillation, in which a spectrally bound function oscillates locally at a rate faster than its fastest Fourier component, has found use in both theoretical and applied areas of optical research.
We show the existence of a complementary phenomenon we term sub-oscillation, in which a spectrally lower bound limited function oscillates locally at an arbitrarily low frequency beyond the lower band limit. We construct a spatially sub-oscillatory optical beam to experimentally demonstrate optical super defocusing i.e. a very fast, exceptional, expansion of a partially blocked light beam.
The relevance of super-oscillations to varied fields such as quantum measurement, optical beam shaping and super-resolution, particle manipulation, electron beam shaping and radio frequency antenna design, suggest that sub-oscillations could find interesting uses in varied fields as well. Our demonstration of super defocusing by itself might be relevant for optical dark-field microscopy.
[1] Y. Eliezer and A. Bahbad, Optica 4, 440 (2017)

Super-resolution (SR) is an effective approach to enhance image spatial resolution. Although many SR algorithms have been proposed by far, little progress has been made to improve resolution for a noisy image. Conventional approaches always adopt the denoising step before applying the SR method to noisy low-resolution images. However, some high-frequency details lose during the denoising step and cannot be restored by the following SR step. Therefore, motivated by the success of deep learning in different computer vision missions, we propose a novel method named Denoising Super-Resolution Deep Convolutional Network (DSR-DCN), to combine both denoising and SR step in a single deep model. The proposed deep model straightly learns an end-to-end mapping from noisy LR space to the corresponding HR space. To equip the proposed network with the capability of blind denoising, Gaussian noise, with a range of standard deviation instead of constant value, is added to each patch of the LR space during training. Experiment results demonstrate that DSR-DCN achieves superior performance and better visual effects than the conventional approaches.

When light passes through a disordered medium, its wavefront is scrambled, resulting in a seemingly random speckle pattern. In the multiple scattering regime, it is commonly assumed that this randomization removes any memory about the original wavefront, effectively destroying all its information content. But as linear elastic scattering is a purely deterministic process, information is not destroyed, but just hidden and redistributed within these patterns. We present an experimental observation of the correlations between reflected and transmitted speckle patterns, which indicate that information can survive even very strong scattering. We show that there are two distinct contributions to the correlation function - a narrow positive peak and a broad negative dip, which depend in a different way on the system parameters. We study the dependence of this correlation on the thickness of the scattering medium and the mean free path of the light in the sample, probing different regimes from ballistic to diffusive scattering. We propose an experimental procedure, based on the ghost imaging technique, that allows to use this correlation for imaging of the objects hidden behind the scattering media.

We present a novel approach for imaging through turbid media that combines the principles of Fourier spatial filtering with single-pixel imaging. We compare the performance of our single-pixel imaging setup with that of a conventional system. We conclude that the introduction of Fourier gating improves the contrast of images in both cases. Furthermore, we show that single-pixel imaging fits better than conventional imaging in vision through turbid media by Fourier filtering.

For different kinds of applications, mainly focused on probing/imaging of complex media, management of light scattering remains a challenge. Numerous studies have proven that the statistical laws followed by the intensity patterns and the polarimetric behaviour of the scattered field at the speckle scale provide a key solution to discriminate between surface and bulk scattering.
It was shown for totally diffusing media that surface and bulk scattering can be seen as extreme scattering regimes. For these two regimes, exact electromagnetic calculation can be performed, but this requires a deterministic knowledge of the medium (surface profile, inhomogeneity function) under study. Furthermore these exact models are time and memory consuming, which reduces the analysis to samples with small dimensions.
Within this framework statistical optics provide solutions which allow to simplify the problem. As an illustration, in previous studies our group recently proposed to use random phasors matrices to predict the statistical behaviour of surface and bulk scattering patterns in terms of intensity and polarimetric parameters. These phenomenological results were validated by comparison to both exact electromagnetic theories and experimental data, with high agreement.
However in these works only the extreme scattering regimes were addressed while they involve zero or total correlation of the scattering coefficients. In this paper we show how to extend the analysis to intermediary scattering regimes, with a comparison to experiment. Furthermore we propose a simplified model involving a unique correlation parameter in the scattering matrix of a strongly disordered medium. Comparison with experiment emphasizes the validity of this model to predict the statistical behavior of the speckle patterns and their polarization properties, as well as spatial depolarization and temporal repolarization. The parameter is connected with the weight of multiple scattering and allows to consider transition between surface and bulk scattering. This statistical approach provides great help to analyze scattering media in the absence of electromagnetic theories.

We investigate ways to improve image resolution and contrast in scatter-plate microscopy by image deconvolution and speckle pattern manipulation. Scatter-plate microscopy uses a single diffusively scattering element instead of a complex lens system to record high resolution images with almost arbitrary magnification. The image of the sample is acquired by cross-correlating the speckle pattern of a point source and the speckle pattern of the incoherently illuminated sample. The working principle is restricted by the finite range of the optical memory effect and by the quality of the light source used to approximate a point source (in our case a single mode fibre). With a deconvolution method using the autocorrelation of the point source speckle pattern as the filter function, describing the relationship between the acquired image and the original object, it is possible to compensate partially the deviation of the used point source from an ideal one. The influence of the restricted range of the memory effect can be reduced by manipulating the sample’s speckle pattern.

The combined approach including experiments (Mueller polarimetry) and theory (differential Mueller matrix formalism) for the studies of anisotropic scattering media was tested on the model system of human skin. Custom-build Mueller polarimetric microscope was used for the studies of histological cuts of full-thickness skin equivalents generated from epidermal keratinocytes forming a multilayered epidermis on top of collagen I hydrogel with dermal fibroblasts. The sets of fixed unstained tissue cuts of different thicknesses (5μm - 30μm) were measured in transmission configuration. The values of polarimetric (dichroism and retardance) and depolarization parameters were calculated by applying pixel-wise the logarithmic decomposition of Mueller matrices. The parabolic dependence of depolarization parameters and linear dependence of polarimetric parameters on thickness, as predicted by theory, was confirmed by measurements. It proves that phenomenological modeling of complex anisotropic scattering medium (e.g., biological tissue) may effectively disentangle the polarimetric and depolarizing properties of the system understudies and may be used for analysis and diagnostics of tissue.

This paper discusses on off-axis digital holography applied to quantitative imaging of flows. The close link between phase measurement and measurands of interest is discussed. Numerical processing of digital holograms and phase retrieval is summarized. The paper presents different architectures that can be found in literature according to different operating modes: speckle-free mode, speckle mode, reduced-sensitivity, and combined approaches.

Lensless color microscopy is a recent 3D quantitative imaging method allowing to retrieve physical parameters characterizing microscopic objects spread in a volume. The main advantages of this technique are related to its simplicity, compactness, low sensitivity of the setup to vibrations and the possibility to accurately characterize objects. The cost-effectiveness of the method can be further increased using low-end laser diodes as coherent sources and CMOS color sensor equipped with a Bayer filter array. However, the central wavelength delivered by this type of laser is generally known only with a limited precision and can evolve because of its dependence on temperature and power supply voltage. In addition, Bayer-type filters of conventional color sensors are not very selective, resulting in spectral mixing (crosstalk phenomenon) of signals from each color channel. Ignoring these phenomena leads to significant errors in holographic reconstructions. We have proposed a maximum likelihood estimation method to calibrate the setup (central wavelength of the laser sources and spectral mixing introduced by the Bayer filters) using spherical objects naturally present in the field of view or added (calibration objects). This calibration method provides accurate estimates of the wavelengths and of the crosstalk, with an uncertainty comparable to that of a high-resolution spectrometer. To perform the image reconstruction from color holograms following the self-calibration of the setup, we describe a regularized inversion method that includes a linear hologram formation model, sparsity constraints and an edge-preserving regularization. We show on holograms of calibrated objects that the self-calibration of the setup leads to an improvement of the reconstructions.

We propose a new algorithm for absolute phase retrieval from multiwavelength noisy phase coded diffraction patterns in the task of surface contouring. A lensless optical setup is considered with a set of successive single wavelength experiments. The phase masks are applied for modulation of the multiwavelength object wavefronts. The algorithm uses the forward and backward propagation for coherent light beams and sparsely encoding wavefronts which leads to the complex-domain block-matching 3D filtering. The key-element of the algorithm is an original aggregation of the multiwavelength object wavefronts for high-dynamic-range profile measurement. Numerical experiments demonstrate that the developed approach leads to the effective solutions explicitly using the sparsity for noise suppression and high-accuracy object profile reconstruction.

Quantitative phase imaging (QPI) became an important technique for label-free biomedical imaging suitable particularly for observation of live cell and dry-mass profiling. Extension of this technique to objects immersed in turbid medium is highly desirable with respect to the need of non-invasive observation of live cells in real 3D environments. Coherencecontrolled holographic microscopy is capable of QPI through turbid media owing to coherence gating induced in transmitted-light geometry by low spatial coherence of illumination. Using this approach, QPI of object in turbid medium can be formed both by ballistic and multiply scattered photons. Moreover, the particular QPIs formed by ballistic and scattered photons can be superimposed thus yielding synthetic QPI of substantially improved image quality. We support the theoretical reasoning of the effect by experimental data.

The incoherent imaging properties of ptychography are discussed in this paper. Usually a coherent light source is employed in ptychography for the recording of the diffraction patterns. However, in combination with a curved illumination it is possible to obtain an image quality of the reconstructed images that is equal to the one known from incoherent imaging. The underlying principle and results to demonstrate these findings are presented in this paper. Moreover, it will be shown that consequently not only the coherent speckle noise but likewise the resolution can be increased.

Tomographic diffractive microscopy (TDM) is an imaging technique which allows for recording the complex optical index of unlabelled specimens. It is based on diffraction theory with a spatially coherent illumination and interference demodulation. Different methods have been developped like illumination rotation with fixed sample or sample rotation with fixed illumination. However this last technique is difficult to set up. Hence, we propose a novel reconstruction technique applicable to axisymmetric unlabelled specimens. It consists in a numerical rotation of the Ewald cap of sphere generated by a zero-degree illumination on the sample. Due to the specimen symmetry, we show that the Fourier space can be filled in the direction perpendicular to the axis of symmetry.

A critical issue associated with the clinical translation of fluorescence molecular imaging relates to the reproducibility of the collected measurements. In particular, images acquired from the same target using different fluorescence cameras may vary considerably when the employed systems have markedly different specifications. Methods that standardize fluorescence imaging are therefore becoming necessary for assessing the performance of fluorescence systems and agents and for providing a reference to the data collected. In the work presented herein we propose a composite phantom for integrating multiple targets within the field of view of a fluorescence camera. Each quadrant of this phantom resolves different fluorescence features: (1) sensitivity as a function of the optical properties; (2) sensitivity as a function of the depth from the top surface; (3) resolution of the fluorescence and optical imaging; and (4) cross-talk from the excitation light. In addition, there exist structures in the phantom for assessing homogeneity of the incident illumination. In order to validate our main hypothesis that standardization of fluorescence imaging systems is feasible through imaging such a phantom, we employed two systems of different specifications and quantified all relevant performance metrics. The derived results showcase the feasibility of fluorescence cameras calibration. Additionally, we demonstrate a methodology of comparing fluorescence cameras by means of benchmarking scoring. We expect that such approaches will boost the clinical translation of fluorescence molecular imaging and will allow for the investigation of novel fluorescence agents.

The introduction of optical imaging by using near-infrared (NIR) light shines new light in the field of (oncologic) surgery. The use of non-specific fluorophores, such as Indocyanine Green (ICG) and Methylene Blue (MB) have already shown its value for different applications during image-guided surgery. Both ICG and MB are currently the only fluorophores approved by regulatory agencies for off-label use. ICG improves visibility of several solid tumors, sentinel lymph nodes, biliary ducts and can be used to evaluate tissue perfusion. MB could be used for ureter imaging and neuroendocrine or thyroid tumors detection. Recently, a shift to molecular imaging was made by the introduction of new NIR fluorophores (IRDye-800CW, ZW800-1), which could be conjugated to tumor or structure specific targets, such as proteins, antibodies, antibody fragments or nanoparticles. Several clinical trials showed detection of both tumor and metastases in patients with head-and neck, colorectal, pancreatic, ovarian, and renal tumors. Furthermore, nerve and ureter specific agents are (pre-)clinically evaluated, however more research is necessary to make these agents clinically available. Limitations of using NIR fluorescence imaging during surgery are the lack of quantification of fluorescence signals and limited penetration depth. Further optimization of NIR fluorescence imaging and evaluation of the clinical benefit for the patient are necessary steps to make NIR fluorescence guided surgery general applicable into surgical daily practice.

Near-infrared fluorescence imaging methods have great advantages. They are fast and noninvasive. Using near-infrared photosensitizers, such as indocyanine green, it is possible to evaluate blood flow in real time. These methods find their application in problems of engraftment of skin grafts1 and in the evaluation of the severity of peripheral arterial disease during indocyanine green fluorescence angiography procedure2 . Irradiation and registration of fluorescent images and video was performed using developed video system that consists of a 785-nm laser diode, a broadband source diode, a beam splitter with a dichroic mirror and two digital CMOS cameras for recording color and luminescence images. Indocyanine green fluorescence angiography procedure was performed in 10 diabetic patients with critical lower limb ischemia. To evaluate the soft tissue perfusion of the foot diabetic patients via fluorescence angiography the following parameters have been used: T0m - time to reach maximum intensity after intravenous injection of the indocyanine green; TIm- the onset of fluorescence intensity in the area of interest; Im - the level of the maximum intensity. Regions of interest are different parts of foot near foot. Fluorescence angiography parameters were compared before and after ercutaneous transluminal angioplasty of lower limb arteries. Fluorescence images show the spread of indocyanine green in skin tissue. The degree of the formation of new blood vessels can be evaluated by intensity of fluorescence. Data from all ROI with different fluorescence angiography parameters was collected. There were significant difference in T0m and TIm in different ROI more than 10 sec.

Nowadays imaging the early liver metastases has to be improved in order to have an easier setup than MRI or to be more discriminant than ultrasound between healthy and diseased tissues. Acousto-optic imaging could solve these issues by coupling itself with ultrasound modality: the additional optical contrast would suppress the indetermination on the health of the biological tissue.
Acousto-optic imaging is a multi-wave technique which localizes light in very scattering media thanks to an acoustic wave: the acousto-optic effect creates frequency-shifted light, carrying local information about the insonified volume. The central challenge of acousto-optic imaging is the detection of the frequency-shifted light, because there are only very few modulated photons and they create a speckle pattern. We choose to explore the detection by spectral filtering using the spectral hole burning process in rare earth doped crystal [1].
Spectral hole burning consists in creating a sub-MHz-wide transparency window in the wide absorption spectrum of a rare earth doped crystal: the crystal becomes transparent at the wavelength of the spectral hole and thus can filter the modulated light. This filtering technique is intrinsically immune to speckle decorrelation and therefore well adapted to in vivo imaging.
We use a YAG crystal doped with thulium ions under a magnetic field which increases the lifetime of the spectral hole from 10ms to longer than a minute. We have undertaken a spectroscopic study to optimize the hole preparation sequence. The long lifetime simplifies the optimization of fast imaging sequences, making real-time acousto-optic imaging reachable. We will present the first acousto-optic images achieved with a long-lived spectral filter in Tm:YAG, in a scattering medium.
[1] Li, Y., Zhang, H., Kim, C., Wagner, K. H., Hemmer, P., & Wang, L. V. (2008). Pulsed ultrasound-modulated optical tomography using spectral-hole burning as a narrowband spectral filter. Applied physics letters, 93(1), 011111.

In this paper, a hybrid method of in-line and off-axis digital holography is proposed. Off-axis digital hologram and in-line hologram are recorded. The approximate phase distributions in the recording plane are obtained by constrained optimization approach from the off-axis hologram, and they are used as the initial value in the iterative procedure of the phase retrieve of in-line hologram. For static objects, the proposed method can be implemented with a single laser and dual shots. For dynamic objects, it can be implemented with dual-wavelength lasers and a single shot. It can achieve high-resolution, wide field-of-view holographic imaging.

We present a phase imaging system using a novel non-interferometric approach. We overcome the limitations in spatial resolution, optical efficiency, and dynamic range that are found in Shack-Hartmann sensors. To do so, we sample the wavefront using a digital micromirror device. A single lens forms a time-dependent light distribution on its focal plane, where a position detector is placed. Our approach is lenslet-free and does not use any kind of iterative or unwrap algorithm to recover the phase information. The validity of our approach is demonstrated by performing both aberration sensing and phase imaging of transparent samples.

Phase Diversity (PD) is an unconventional imaging technique which uses two or more distorted views of an object to perform wavefront sensing and/or to clarify the object. In 1990 it was used to remove the flaw in the Hubble Space Telescope. A major advantage of PD is that it needs no auxiliary hardware, like a guide star or a Shack-Hartmann wavefront sensor. We review a personal path in the discovery and the use of phase diversity. That path started in 1974 with the removal of raster lines in digital-based satellite images and has led to the real-time removal of aberrations in high-performance, ground-based telescopes, among other applications. PD could be used in cell phones which maintain good image quality by changing the camera's optics. The recorded video and the changes in the camera's optics are the necessary observations needed to improve the video, with software called sequential diversity imaging.

When light propagates through highly disordered media such as biological tissue, multiple scattering prevents light from reaching depths much larger than the transport mean free path, making the material opaque. This poses a problem for Raman spectroscopy in biological media, where in order to obtain spontaneous Raman signal they need to work in the superficial region of the material or increase the pump power, which is not always a safe option. In this work we show that wavefront shaping techniques can significantly increase light penetration through opaque media, thus allowing detection of Raman scattered light of materials deep inside an opaque medium, avoiding the increase of the pump power.
Wavefront shaping techniques are capable of manipulating the amplitude and/or phase of a light beam, which allows control over light propagation through such media. Wavefront shaping was originally proposed to focus light through a scattering material [1], and was recently shown capable of increasing light penetration in very thin (8 μm) scattering layers [2]. But efficiently delivering light at larger depths (~100 μm) in strongly scattering material, with optical densities comparable to thick biological tissues, is still an unsolved problem.
In this work we use a fast Digital Micromirror Device (DMD) to control the phase profile of the pump light incident on the sample, made of two layers of different strongly scattering materials (TiO2 and Hidroxyapatite). Using the transmitted light as feedback, an iterative algorithm adapts the phase pattern controlled by the DMD maximizing the penetration depth of the incident light. A spectrometer collecting the reflected light quantifies the depth at which the pump light is reaching by analysing the spontaneous Raman signal of the inner layer of the sample. We show an increase of 40% in the Raman signal collected from the inner material when the wavefront is optimized, equivalent to 40% deeper penetration of the pump light, given the linear characteristics of spontaneous Raman scattering.
This result shows the usefulness of wavefront shaping techniques to increase the penetration depth of light, improving the applicability of Raman spectroscopy in thicker materials. This is of enormous interest in the fields of non-invasive breast cancer diagnosis, light-activated cancer drugs or white LEDs where penetration depth of light is limited by scattering and applied power needs to be in the safe regime.
[1] I.M. Vellekoop, and A.P Mosk, Optics Letters 32, 2309 (2007).
[2] W. Choi, et al. Scientific Reports 5, 11393 (2015).

CIAO is a Compact Innovative Adaptive Optic system for 0.5 to 2 m telescopes.
Pic du Midi observatory is known for the quality of its planetary images thanks to the site quality and the long experience of the team. The technique is still improving; our last step is the development of an adaptive optics system. This compact and affordable system, developed in collaboration with Observatoire de Paris could also interest other observatories with telescopes in the 0.5 to 2m range.
We are able to analyze the wave front of the target at 1000 Hz, with a rejection bandwidth of correction up to 100 Hz on bright targets. On fainter targets, the system can still run slower, it is used in this case as an active optics to compensate the static defaults of the telescope or slow evolution of the air turbulence.
The first tests on the sky were at the end of October. The device worked as expected and the results are very encouraging. We have been able to improve the image quality by a factor 4 on several targets such as stars and the planet Mars.
We will present in this conference how an adaptice optics system works, the prototype architecture and how we implemented it on the Nasmyth focal plane of the 1m diameter telescope at Pic du Midi. Many results will be presented including video showing in realtime the gain of the adaptive optics. The best known images of Mars in this orbit situation will be shown.
We thank PNP (Programme National de Planétogie), Paris Observatory scientific Council and IMCCE (Institut de Mécanique Céleste et de Calcul des Ephémérides) for their financial support and Jean-Luc Dauvergne for his help on the project.

This work shows the interest of combining polarimetric and light-field imaging. Polarimetric imaging is known for its capabilities to highlight and reveal contrasts or surfaces that are not visible in standard intensity images. This imaging mode requires to capture multiple images with a set of different polarimetric filters. The images can either be captured by a temporal or spatial multiplexing, depending on the polarimeter model used. On the other hand, light-field imaging, which is categorized in the field of computational imaging, is also based on a combination of images that allows to extract 3D information about the scene. In this case, images are either acquired with a camera array, or with a multi-view camera such as a plenoptic camera. One of the major interests of a light-field camera is its capability to produce different kind of images, such as sub-aperture images used to compute depth images, full focus images or images refocused at a specific distance used to detect defects for instance. In this paper, we show that refocused images of a light-field camera can also be computed in the context of polarimetric imaging. The 3D information contained in the refocused images can be combined with the linear degree of polarization and can be obtained with an unique device in one acquisition. An example illustrates how these two coupled imaging modes are promising, especially for the industrial control and inspection by vision.

We introduced two continuous-wave terahertz iterative phase-contrast imaging methods. In-line digital holography has the capability to reconstruct the amplitude and phase distributions simultaneously. It is a non-destructive, high-resolution, full-field dynamic phase-contrast imaging technique. Ptychography can reconstruct the complex amplitude distribution of the transmission object from the overlapped diffraction patterns. Both methods can achieve phase-contrast imaging, and are suitable for terahertz region. In this paper, both Gabor in-line holographic and ptychographical configurations are investigated from algorithms to experiments. For in-line holography, the use of extrapolation, synthetic aperture, sub-pixel shifting and multi-plane imaging are introduced to improve the resolution and reconstruction accuracy. For ptychography, we obtained the ptychographical reconstruction results of a polypropylene alphabet sample, which provides a new imaging method for terahertz phase-contrast imaging.

We have developed a method of the terahertz (THz) solid immersion microscopy for the reflection-mode imaging of soft biological tissues. It relies on the use of the solid immersion lens (SIL), which employs the electromagnetic wave focusing into the evanescent-field volume (i.e. at a small distance behind the medium possessing high refractive index) and yields reduction in the dimensions of the THz beam caustic. We have assembled an experimental setup using a backward-wave oscillator, as a source of the continuous-wave THz radiation featuring λ= 500 μm, a Golay cell, as a detector of the THz wave intensity, and a THz SIL comprised of a wide-aperture aspherical singlet, a truncated sphere and a thin scanning windows. The truncated sphere and the scanning window are made of high-resistivity float-zone silicon and form a unitary optical element mounted in front of the object plane for the resolution enhancement. The truncated sphere is rigidly fixed, while the scanning window moves in lateral directions, allowing for handling and visualizing the soft tissues. We have applied the experimental setup for imaging of a razor blade to demonstrate the advanced 0:2λ resolution of the proposed imaging arrangement. Finally, we have performed imaging of sub-wavelength-scale tissue spheroids to highlight potential of the THz solid immersion microscopy in biology and medicine.

Terahertz pulsed imaging has attracted considerable interest for revealing the stratigraphy and hidden features of art paintings. The reconstruction of the stratigraphy is based on the precise extraction of THz echo parameters from the reflected signals. Several historical panel paintings and wall paintings have been well studied by THz reflective imaging, in which the detailed stratigraphy has been successfully revealed. To our knowledge, however, the stratigraphy of oil paintings has not been clearly uncovered by THz imaging, since the paint layers in an oil painting on canvas, especially for the 16th and 17th century art works, are usually very thin (~10 μm) in the THz regime. Therefore, in order to improve the performance of THz imaging, advanced signal-processing techniques with higher depth-resolution are still needed. In this study, THz reflective imaging is employed to reveal for the first time the detailed stratigraphy of a 17th century Italian oil painting on canvas. The paint layers on the supporting canvas are very thin in the THz regime, as the THz echoes corresponding to the stratigraphy totally overlap in the first cycle of the reflected THz signal. THz sparse deconvolution based on an iterative shrinkage algorithm is utilized to resolve the overlapping echoes. Based on the deconvolved signals, the detailed stratigraphy of this oil painting on canvas, including the varnish, pictorial, underdrawing, and ground layers, is successfully revealed. The THz C- and B-scans based on the THz deconvolved signals also enable us to reveal the features of each layer. Our results thus enhance the capability of terahertz imaging to perform detailed analysis and diagnostics of historical oil paintings on canvas with foreseen applications for the study of the artist’s technique and for authentication.